The invention relates to a droplet ejection device having a nozzle head with a plurality of ejection units each of which comprises a nozzle, a duct connected to the nozzle, and an electromechanical transducer arranged to create a pressure wave in a liquid in the duct so as to expel a droplet of the liquid from the nozzle, the device further comprising an electronic control circuit arranged to apply control signals to the transducers and to receive detection signals that are generated in the transducers in response to the transducer being exposed to pressure fluctuations in the liquid.
Such a droplet ejection device may for example be employed in an ink jet printer or a 3D printer. EP 1 378 359 A1 describes an ink jet printer having an ejection device of the type indicated above, wherein the transducers are formed by piezoelectric transducers. When a voltage is applied across electrodes of the transducer, the piezoelectric material is caused to deform, whereby the volume of the duct is changed and a pressure wave is induced in the liquid ink that is contained in the duct. Conversely, when the transducer is subject to pressure fluctuations in the liquid ink, which may be caused for example by an acoustic wave still present in the duct after the nozzle has been fired, these pressure fluctuations will induce voltage fluctuations which may be detected in the electronic control system. In the known printer, this effect is utilized for monitoring the functioning of the droplet ejection devices.
In general, a detection signal from a transducer as a result of pressure fluctuations is much smaller than a control signal, or an actuation pulse, that is applied to the transducer in order to expel a droplet. It is therefore common practice to connect the transducer either to a control circuit for applying an actuation pulse or to a detection circuit for detecting the pressure fluctuations. This restricts the time window for measuring these fluctuations, since it is necessary to switch from one circuit to another. Moreover, the pressure fluctuations during actuation cannot be measured, although the pressure fluctuations during actual actuation may contain very valuable information on the status of the ejection unit.
It is an object of the present invention to provide a droplet ejection device of the type indicated above, wherein fluctuations can be measured during the application of an actuation pulse.